1. Technical Field
The present disclosure relates to an antenna, in particular, to stand-alone multi-band antenna.
2. Description of Related Art
Most of conventional embedded antennas are designed to be planar inverted-F antenna (PIFA) or monopole antenna, and these two-type antennas must have corresponding ground plates to radiate, such that the antenna can have the good impedance matching and the good radiation performances. Generally speaking, the antenna ground plate is usually the system ground plate of the electronic device, and the system ground plate is used for the layout of the electronic elements. When the displacement of the electronic elements on the system ground plate is changed, the dimension and the shape of the system ground plate may change as well. In other words, the impedance and radiation performances of the antenna will be influenced corresponding to the system ground plate.
For the antenna designer, he or she not only designs the antenna pattern, but also takes the other factors, such as the dimension and the shape of the system ground plate, into the design consideration, such that the design complexity of the antenna is increased dramatically. In the development of the current antenna design, it is understood that stand-alone antenna is gradually applied in the electronic device of the network communication field. The advantage of the stand-alone antenna is that the stand-alone antenna can generate the required operating band without any additional antenna ground plate. However, the stand-alone antenna is easy to be affected by the ambient environment, and in particular, when the metal element exists nearby the stand-alone antenna, the impedance and radiation performances of the stand-alone antenna would be affected dramatically.
Some stand-alone antennas with multi-band operation have been published. Taiwanese Patent No. M377714 disclosures the PIFA-typed stand-alone antenna with multi-band operation having dual paths. Furthermore, the conventional multi-band antenna has the simple structure, and therefore the conventional multi-band antenna is easy to be implemented. However, according to the properties of the planar inverted-F antenna, it is known that the current distribution on the terminal end of the resonant path is weaker than that on the other location, in other words the electrical field on the terminal end of the resonant path is larger than that on the other location, and therefore the fringing-field effects will be generated. When the object (especially, the metal object) is nearby the conventional multi-band antenna, the fringing-field of the conventional multi-band antenna and the nearby object are mutually coupled to each other, and therefore the impedance and radiation performances of the conventional multi-band antenna are dramatically affected. Due to the properties of the conventional multi-band antenna, the arrangement location of the conventional multi-band antenna is limited by the inner environment of the electronic device, and the practical application value of the conventional multi-band antenna is thus reduced.